A multifunction warming device for perioperative use includes a clinical garment with two or more convective warming apparatuses supported on the inside of the garment. At least one convective apparatus has separately inflatable sections, each for enabling a particular mode of warming.
In this specification, use of the term “convective” to denote the transfer of heat from a device to a body refers to the device's principal mode of heat transfer, it being understood that heat may at the same time be transferred from the device to the body by conduction and radiation, although not to the degree of convection.
Convective devices that transfer heat to a human body are known. For example, there are devices that receive a stream of pressurized, warmed air, inflate in response to the pressurized air, distribute the warmed air within a pneumatic structure, and emit the warmed air onto a body to accomplish such objectives as increasing comfort, reducing shivering, and treating or preventing hypothermia. These devices are typically called “convective thermal blankets” or “covers”; for convenience, in this discussion and the following specification, they shall be called, simply, “thermal blankets.” Arizant Healthcare Inc., the assignee of this application, makes and sells such devices under the BAIR HUGGER® brand. One such device is the Model 522 Upper Body Blanket.
Thermal blankets have been specifically designed for particular deployments where therapeutic warming is indicated. Three representative thermal blankets known in the prior art are shown in FIGS. 1A-1D. A “full body” thermal blanket 10 is shown in FIG. 1A. The full body thermal blanket is adapted to lie upon a person and to extend longitudinally along the body of the person in order to cover substantially the person's entire body, from near the ankles or feet up to the neck. A “lower body” thermal blanket 12 is shown in FIG. 1B. The lower body thermal blanket 12 is adapted to lie upon the person and to extend longitudinally along the body of a person in order to cover the person's lower body, from near the ankles or feet up to the waist or pelvis of the person. An “upper body” thermal blanket 15 is illustrated in FIGS. 1C and 1D. The upper body thermal blanket 15 has a bow-tie shape that is adapted to lie upon and extend transversely across the upper body of a person in order to cover the person's chest and extended arms. A head drape 16 may be formed on or attached to the upper body thermal blanket 15 for draping over the head 17 of a person in order to retain warmed air expelled through the blanket 15 about the head to aid in therapeutic warming during surgery. When fed a stream of warmed pressurized air, each of the thermal blankets 10, 12, 15 inflates and distributes the air within itself. While the thermal blanket lies on the person, the warmed pressurized air flows through apertures or interstices in a permeable surface of the thermal blanket which faces the person. These thermal blankets may have one, two, or more inlet ports 18 through which an air hose 19 provides warmed pressurized air from a heater/blower unit (not shown in these drawings).
The construction of prior art thermal blankets is well understood. Examples of specific constructions are given in U.S. Pat. No. 5,620,482, U.S. Pat. No. 5,443,488, U.S. Pat. No. 5,360,439, and U.S. Pat. No. 5,304,213. See also U.S. Pat. No. 5,974,605.
An invention covering a warming device is disclosed in the referenced Publication No. WO 2003/086500 wherein a clinical garment such as a robe or gown is adapted to support a convective apparatus in order to warm a person wearing the garment for comfort and mobility of the person. An invention covering a multifunction warming device for perioperative use is described in the referenced Publication US 2006/0122671 wherein a warming device is constituted of a clinical garment and a convective apparatus adapted for comfort and therapeutic warming that is supported on the inside surface of the garment.
The term “perioperative” is defined in the PDR Medical Dictionary, Second Edition, (Medical Economics Company, 2000), as “around the time of operation.” The perioperative period is characterized by a sequence including the time preceding an operation when a patient is being prepared for surgery (“the preoperative period”), followed by the time spent in surgery (“the intraoperative period”), and by the time following an operation when the patient is closely monitored for complications while recovering from the effects of anesthesia (“the postoperative period”).
According to Mahoney et al. (Maintaining intraoperative normothermia: A meta-analysis of outcomes with costs. AANA Journal. 4/99; 67, 2:155-164.), therapeutic warming is employed during at least the intraoperative period in order to prevent or mitigate effects that result from hypothermia. In fact, it is increasingly manifest that maintenance of normothermia perioperatively enhances the prospects for a quick, successful recovery from surgery. For example, maintenance of perioperative normothermia appears to be a factor in decreasing the incidence of surgical wound infections in patients undergoing colorectal surgery, (Kurz A, Sessler D I, Lenhardt R. Perioperative normothermia to reduce the incidence of surgical-wound infection and shorten hospitalization. Study of Wound Infection and Temperature Group. N Engl J Med. May 9, 1996; 334(19):1209-1215). Other studies suggest that maintenance of perioperative normothermia improves surgical outcomes at low cost, (Harper C M, McNicholas T, Gowrie-Mohan S. Maintaining perioperative normothermia. BMJ. Apr. 5, 2003; 326(7392):721-722). The effectiveness of therapeutic warming depends upon delivery of enough heat to a patient's body to raise the patient's core body temperature to, or maintain it within, a narrow range, typically around 37° C. This range is called “normothermic” and a body with a core temperature in this range is at “normothermia.” Hypothermia occurs when the core body temperature falls below 36° C.; mild hypothermia occurs when core body temperature is in the range of 34° C. to 36° C. Therefore, “perioperative therapeutic warming” is warming therapy capable of being delivered during one or more of the perioperative periods for the prevention or treatment of hypothermia.
Therapeutic warming is contrasted with “comfort warming” which is intended to maintain or enhance a patient's sense of “thermal comfort”. Of course, therapeutic warming may also comfort a patient by alleviating shivering or a feeling of being cold, but this is a secondary or ancillary effect; and, comfort warming may have some therapeutic effect. However, even though thermal comfort is a subjective notion, environmental conditions that produce a sense of thermal comfort in a population of human beings are known and well tabulated. For example, Fanger (Thermal Comfort: Analysis and Applications of Environmental Engineering, Danish Technical press, Copenhagen, 1970) defines thermal comfort as “that condition of mind which expresses satisfaction with the thermal environment.” Even when a patient is normothermic, less than ideal environmental conditions can result in acute feelings of discomfort. Under normothermic conditions, thermal comfort is largely determined with reference to skin temperature, not core body temperature. Comfort warming is warming applied to a patient to alleviate the patient's sense of thermal discomfort.
Therapeutic warming may be indicated during any one or more of the perioperative periods. For example, for a short operation in a surgery with no warming equipment available, a person may be warmed preoperatively in a preparation area to raise mean body temperature to a level higher than normal in order to store enough thermal energy to maintain normothermia, without heating, intraoperatively. After surgery, it may be necessary to apply therapeutic warming in a recovery area to raise the core temperature to normothermia and maintain it there for a period of time while anesthesia wears off. Alternatively, for a long surgery in an arena with heating equipment available, a person may be warmed for comfort before surgery and warmed therapeutically during and after surgery.
Therapeutic warming is typically provided by convective devices such as the thermal blankets shown in FIGS. 1A-1D. An example of use of a full body thermal blanket for therapeutic warming is found in U.S. Pat. No. 6,524,332, “System and Method for Warming a Person to Prevent or Treat Hypothermia”, commonly owned with this application. Comfort warming by convective means is described in the referenced Publication No. WO 2003/086500.
When delivered by convective devices, therapeutic warming is distinguished from comfort warming by intended effects and by the parameters of heat delivery that produce those effects. In this regard, a convective warming system typically includes a source of warmed pressurized air (also called a heater/blower unit, a forced-air warming unit, a heater unit, etc.), a convective device (which is, typically, inflatable), and a flexible conduit or air hose connecting the heater/blower unit with the convective device. Use of such a system for a particular type of warming requires delivery of warmed air through a convective device at parametric values that achieve a particular objective. For example, for comfort warming, the temperature at the hose end, prior to the air entering the convective device, may range from ambient to 42° C. (WO 2003/086500 at page 11, lines 24-26). The conditions by which a convective device such as a thermal blanket produces thermal comfort in normothermic individuals at steady state are significantly different from those necessary to treat hypothermia. Typically the conditions for thermal comfort are met in a system with a relatively low capacity heater/blower unit that delivers a stream of air at one combination of pressure and temperature, while those in a therapeutic warming system are achieved with a relatively high capacity heater/blower unit that delivers a stream of air at another combination of pressure and temperature. Alternatively, a single heater/blower unit may be provided with controls that enable it to adjust the combination of air pressure and temperature in order to vary its operation between support of comfort and therapeutic warming.
Health care cost is an issue of national importance. The cost of warming perioperatively is directly related to the number of perioperative periods in which a person is warmed; the cost increases when different warming apparatus are used in different periods to accomplish different goals. Mobility, comfort, and therapy have recently been combined in warming configurations described in the related applications that are identified above. However, there is currently no single warming device configuration that affords all of the options for therapeutic warming that are available in the set of thermal blankets illustrated in FIGS. 1A-1D.
For example, the upper body thermal blanket 15 shown in FIGS. 1C and 1D is frequently used during thoracic, abdominal and pelvic surgery. As is known, a patient's core body temperature can drop to hypothermic levels quickly during such surgery. To prevent or mitigate the effects of hypothermia, an upper body blanket might be deployed for therapeutic warming during the surgery, especially if it is lengthy. If warmed preoperatively with a comfort warming device described in WO 2003/086500, or with a perioperative warming device described in US 2006/0122671, the patient will have the warming device on up to the time when surgery commences. But, in both cases, the clinical garment is removed from the patient prior to surgery in order to provide access to the surgical site and to the patient's upper body for therapeutic warming. Concurrently, an upper body thermal blanket must be unpackaged, made ready and deployed warming during for surgery. Following surgery, warming may be indicated for therapy (mitigation of hypothermia, for example) or comfort, in which case either the warming device used preoperatively, another warming device, or a thermal blanket must be deployed on the patient. Manifestly, substantial convenience and a significant reduction in cost would result from perioperative use of a single multifunction warming device capable of clothing a patient and providing comfort warming preoperatively, manifold therapeutic warming intraoperatively (including during thoracic, abdominal and pelvic surgery), and optional therapeutic or comfort warming postoperatively.